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991.
Du
an Uhrín Gyula Batta Victor J. Hruby Paul N. Barlow Katalin E. Kvr 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2)
An enhanced version of the X(ω1) half-filtered TOCSY experiment for measurement of long-range heteronuclear coupling constants is proposed which yields high-quality spectra with substantially increased sensitivity and resolution. The modified method features gradient-enhanced X filtering sequences, broadband homonuclear decoupling duringt1, optional1JXHscaling in theF1domain, and gradient coherence selection in combination with the sensitivity-enhanced protocol for the TOCSY transfer. These modifications extend the applicability of the method—coupling constants can be measured accurately for natural abundance samples at low concentrations and for compounds yielding complex spectra. Computer-aided analysis of E.COSY-type multiplets is applied for the determination of heteronuclear long-range coupling constants. 相似文献
992.
Bootstrap bandwidth selection in kernel density estimation from a contaminated sample 总被引:4,自引:0,他引:4
In this paper we consider kernel estimation of a density when the data are contaminated by random noise. More specifically
we deal with the problem of how to choose the bandwidth parameter in practice. A theoretical optimal bandwidth is defined
as the minimizer of the mean integrated squared error. We propose a bootstrap procedure to estimate this optimal bandwidth,
and show its consistency. These results remain valid for the case of no measurement error, and hence also summarize part of
the theory of bootstrap bandwidth selection in ordinary kernel density estimation. The finite sample performance of the proposed
bootstrap selection procedure is demonstrated with a simulation study. An application to a real data example illustrates the
use of the method.
This research was supported by ‘Projet d’Actions de Recherche Concertées’ (No. 98/03-217) from the Belgian government. Financial
support from the IAP research network nr P5/24 of the Belgian State (Federal Office for Scientific, Technical and Cultural
Affairs) is also gratefully acknowledged. 相似文献
993.
In this paper a probability maximization model of a stochastic linear knapsack problem is considered where the random variables consist of several groups with mutually correlated ones. We propose a solution algorithm to the equivalent nonlinear fractional programming problem with a simple ranking method. This approach will be effectively applied to one of the portfolio selection problems. 相似文献
994.
针对蚁群算法在寻优过程中容易出现停滞现象,同意在该算法中引入免疫机制,将待求解问题看成抗原,而问题的解看成抗体,通过基于浓度的选择机制和多样性保持策略来提高蚁群算法的全局搜索能力和避免停滞现象.对TSP问题的仿真实验结果表明,该算法极大地提高了搜索能力和避免了停滞现象. 相似文献
995.
Thorsten Kleinjung. 《Mathematics of Computation》2006,75(256):2037-2047
The general number field sieve (GNFS) is the asymptotically fastest algorithm for factoring large integers. Its runtime depends on a good choice of a polynomial pair. In this article we present an improvement of the polynomial selection method of Montgomery and Murphy which has been used in recent GNFS records.
996.
Mino Yang 《Journal of Molecular Spectroscopy》2006,239(1):108-114
Intensity pattern of the vibronic transitions of a molecular dimer consisting of two molecules interacting through the Coulombic coupling is theoretically studied using a reduced density-matrix approach. The monomeric molecules are assumed to be electronic two-state systems. A single vibration mode with a high frequency and a continuous distribution of low-frequency phonons represented by the Ohmic spectral density are coupled to the electronic transition of the respective molecules. The spin-Boson model is employed to include the effect of electron-vibration and electron-phonon couplings. The intermolecular Coulombic coupling is assumed to be weak (inducing the Förster type of energy transfer process). It is found that, in addition to the well-known excitonic shifts, the intensity of the vibronic side bands reduces with the intermolecular coupling strength in the J-aggregate type of dimer while it increases in the H-aggregate type. When the vibronic bands are blurred by the broadening resulting from the coupling of the electrons to the continuous distribution of the phonons, the absorption line shape shows a wide range of variation depending on the strength of the intermolecular coupling. 相似文献
997.
When designing an open storage system for bulk material like coal or iron ore, operational and investment parameters are to be considered. Those inputs are always managed by engineers and prolific literature can be found. But entering into environmental parameters like wind erosion, few methodologies are available, US EPA being one of the most extensive. This source is focused on certain conditions of wind direction, pile shape, etc. what sometimes are not matching the most interesting way of storing the material: area restrictions, stacking means, etc. Based on state of the art computational fluid dynamics (CFD) software, in this case we have used ANSYS CFX 5.7., modelling system was developed and compared to EPA results for conical and oval with flattop piles. After adjusting the calculation process and selecting the most effective variables, the semicircular shape was studied finding that for the same amount of material stored, lower emissions and wind erosions are to be expected; however depending on wind direction higher values of friction per surface unit are found but due to its higher volume of storage per square metre, the balance is positive to the semicircular pile. 相似文献
998.
With uncorrelated Gaussian factors extended to mutually independent factors beyond Gaussian, the conventional factor analysis is extended to what is recently called independent factor analysis. Typically, it is called binary factor analysis (BFA) when the factors are binary and called non-Gaussian factor analysis (NFA) when the factors are from real non-Gaussian distributions. A crucial issue in both BFA and NFA is the determination of the number of factors. In the literature of statistics, there are a number of model selection criteria that can be used for this purpose. Also, the Bayesian Ying-Yang (BYY) harmony learning provides a new principle for this purpose. This paper further investigates BYY harmony learning in comparison with existing typical criteria, including Akaik’s information criterion (AIC), the consistent Akaike’s information criterion (CAIC), the Bayesian inference criterion (BIC), and the cross-validation (CV) criterion on selection of the number of factors. This comparative study is made via experiments on the data sets with different sample sizes, data space dimensions, noise variances, and hidden factors numbers. Experiments have shown that for both BFA and NFA, in most cases BIC outperforms AIC, CAIC, and CV while the BYY criterion is either comparable with or better than BIC. In consideration of the fact that the selection by these criteria has to be implemented at the second stage based on a set of candidate models which have to be obtained at the first stage of parameter learning, while BYY harmony learning can provide not only a new class of criteria implemented in a similar way but also a new family of algorithms that perform parameter learning at the first stage with automated model selection, BYY harmony learning is more preferred since computing costs can be saved significantly. 相似文献
999.
Many researchers see the need for reject inference in credit scoring models to come from a sample selection problem whereby a missing variable results in omitted variable bias. Alternatively, practitioners often see the problem as one of missing data where the relationship in the new model is biased because the behaviour of the omitted cases differs from that of those who make up the sample for a new model. To attempt to correct for this, differential weights are applied to the new cases. The aim of this paper is to see if the use of both a Heckman style sample selection model and the use of sampling weights, together, will improve predictive performance compared with either technique used alone. This paper will use a sample of applicants in which virtually every applicant was accepted. This allows us to compare the actual performance of each model with the performance of models which are based only on accepted cases. 相似文献
1000.
M. Sanchis 《Set-Valued Analysis》2004,12(3):319-328
We characterize locally pseudocompact groups by means of the selection theory. Our result is the selection version of the
well-known Comfort—Ross theorem on pseudocompactness which states that a topological group is pseudocompact if and only its
Stone—Čech compactification is a topological group. 相似文献